<!DOCTYPE HTML>
<html>

<head>
  <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
  <title>prompt</title>
  <script type="text/javascript">
    function rec() {
      var score; //score变量，用来存储用户输入的成绩值。
      score = prompt("输入你的成绩");
      if (score >= 90) {
        document.write("你很棒!");
      } else if (score >= 75) {
        document.write("不错吆!");
      } else if (score >= 60) {
        document.write("要加油!");
      } else {
        document.write("要努力了!");
      }
    }
  </script>
</head>

<body>
  <input name="button" type="button" onClick="rec()" value="点击我，对成绩做评价!" />
</body>

</html>